Investment ring



March 12, 1940. s, H.

. INVESTMENT [RING Filed April 8, 1938 Patented Mar. 12, 1940 UNiTEDSTATE OFEQE 2 Claims.

This invention, an expansible investment ring, is primarily designed forcasting removable bridges for artificial dentures, and the improvementin this invention resides in the expansible feature which obviatesbreakage of the ring through the medium of contraction caused by suddencooling of the ring relative to the investment, when removed from thefurnace.

In the usual process of casting removable W bridges, the working modelof the denture has the bridge formed in wax thereon together withnecessary gates, and is placed in a non-expansible ring and invested inthe ring, after which the assembly is placed in a furnace and heated toabout 1600 C., which burns out all of the wax, leaving a mold of thebridge with its gates and vents.

When this type of investment ring is removed from the furnace and placedin the centrifugal 20 casting machine and centrifuged, the investmentring cools very quickly while the investment remains at a very hightemperature, therefore the ring contracts about the substantiallynon-contracting investment. The result is that the ring I 25 usuallybreaks and is then unfit for further use.

This invention provides an investment ring which can be used repeatedly,since the ring may be eased up as soon as the investment has set, orwhen it is taken from the furnace; and after easing up, contraction dueto cooling will not cause the ring to break, since the allowance forexpansion compensates fully for the difference in contraction betweenthe ring and its investment.

Although this ring is specifically designed for 3.3 dental castingprocesses, it can be used to advantage for other casting processes.

The main object of the invention therefore, is to provide an investmentring with means to compensate for unlike contraction between the ringand its investment.

Another object of the invention is to provide an investment ring with aneccentric connecting pin or pintle which may be removed at will forremoving the investment, or eased up to com- 45 pensate for thermalcontraction about an investment which has not contracted, whereby thebreaking of the investment ring under tensional stresses is obviated.

In describing the invention, reference will be 50 had to theaccompanying drawing of which:

Fig. l is a plan view of the invention showing in dotted lines abuilt-up Working model in position for investing.

Fig. 2 is a front elevation of Fig. l.

55 Fig. 3 is a section taken on line 3-3 of Fig. 1.

Fig. 4 is a fragmentary view taken on line 4-4 of Fig. 1.

The investment ring in its usual form consists of a ring Hl terminatingat its ends II and I2 7 in a suitable releasable connection, using apin, 5* sleeve, or other means to connect the ends, the

ring having a clasp is for attachment to a cen,

trifugal casting machine arm, (not shown).

This invention incorporates the structure just described, but ismodified in the connecting means 10' by the provision of means forpositively releasing the tension to an exact degree after the investmenthas set, to prevent breaking of the ring due to unequal expansionand'contraction between the ring and its invesement during heating andcooling of the assembly, while maintaining a diameter suitablysupporting the investment.

This improvement is illustrated as consisting of the pintle sleeves itand iii formed on one terminal end of the ring indicated at l2, and aninterposed pintle sleeve Ni formed on the other terminal H, the portionsll and [8 of the terminal end ll interlapping within the terminal end l2as shown.

The pintle sleeves M, 15 and It all have the same inside diameter,although they could be made to vary and still produce the same result solong as the pintle could be removed at will.

The pintle consists of a straight rod bent at right angles to form acombined grip and lever arm i9, and this pin is eoc-entrically turned toa smaller diameter at 2! where it acts within the pintle sleeve l6,whereby, when the arm 19 is in one position, the eccentric 2| permitsthe ring to be expanded to an exact predetermined degree as shown inFig. 2, and when turned to its other position, it retains the ringagainst expansion from its normal investing diameter.

Since the sleeves all have the same diameter, and no part of theeccentric projects diametri- 40 cally beyond the main portion of therod, the pintle may be readily removed for opening the ring for removingthe investment in the usual manner.

It is well known that eccentrics have been used for many purposes,however, this eccentric functions in a new way and provides a differentresult and one which has not been previously applied to investmentrings. It limits the physical expansion of the ring to a degree onlysufficient to compensate for difierence in thermal contraction betweenthe ring and its investment, while still locking the ring to providesupporting means for the investment.

In the process of making the investment and casting the bridge, thepintle is inserted through the pintle sleeves and turned to the positionshown dotted at 22, retaining the ring in its normal investing position.

The model 23, suitably built up with wax for bridge, gates and vents, isplaced Within the ring and the ring filled with investing material,which is allowed to suitably set, after which the ring with itsinvestment is placed in a furnace and heated to a temperature of about1600 centigrade.

The pintle arm 19 may be turned to position l9 before placing theinvestment with its ring in the furnace, or, immediately upon removalfrom the furnace. This adjustment through eccentric 2| eases up theconnection and permits the ring to open an amount equal to theeccentricity of the pintle, and prevents excess opening of the ring tomaintain support for the investment.

After the ring with its investment has been removed from the furnace,the ring obviously cools very quickly while the investment cools slowly,therefore there is unequal contraction creating a tension on the ringwhen not eased up as just outlined.

Since the ring has been eased up through the agency of the eccentricsufficiently to allow contraction of the ring without acting on theinvestment, no strain is set up in the ring while all of the element ofsupport is maintained, the amount of easing being fixed andnon-variable.

The ring with its investment is placed in the centrifugal castingmachine, (not shown), the metal poured and centrifuged, after which thepintle is removed through the medium of the grip 19, the ring manuallyexpanded, and the investment removed and broken away from the casting.

It will be noted that the rivet heads 24 and the intermediary spacebetween the interlapping members I! and i8 secure the investment in thering during centrifuging while the connection is eased up.

Thus, a releasable, contraction-compensating joint is provided for aninvestment ring.

Having described an operative device and method of casting removablebridges and other types of castings, it will be understood thatvariations in construction and arrangement of parts, which variationsare consistent with the appended claims may be resorted to withoutdetracting from the spirit or scope of the invention, or sacrificing anyof the advantages thereof.

I claim:

1. An investment ring having inter-lapping and terminal ends forminganchorage means for an investment and pintle sleeves of equal diameterformed on the respective terminal ends, and a pintle removable at willand adjustable to two positions and having a main body diameterrotatably fitting within the sleeves of one terminal end, and aneccentric portion of lesser diameter and entirely confined within thediametral limits of the body portion and operating within the sleeve ofthe other terminal end, and a lever arm integral with said pintle foradjustment and removal thereof at will.

2. An investment ring having interlapping terminal ends forminginvestment retaining means, and, pintle sleeves of equal diameter; rivetheads diametrically located relative to said terminal ends and formingadditional retaining means; a pintle having a main portion fitting thepintle sleeves for one terminal end, and an intermediate portion ofsmaller diameter operating in the pintle sleeves for the other terminalend and having a clearance therein substantially equal to thecontractual difference between the investment and the ring whilemaintaining association between the retaining means and the investment;said pintle being completely removable at will to permit excessiveexpansion of the ring to facilitate removal of the ring from theinvestment.

AUGUST S. GRETH.

